The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known. Radar uses electromagnetic energy pulses in much the same way, as shown in Figure 1. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object. The term RADAR is an acronym made up of the words: RAdio (Aim) Detecting And Ranging The term “RADAR” was officially coined as an acronym by U.S. Navy Lieutenant Commander Samuel M. Tucker and F. R. Furth in November 1940. The acronym was by agreement adopted in 1943 by the Allied powers of World War II and thereafter received general international acceptance. [1] It refers to electronic equipment that detects the presence of objects by using reflected electromagnetic energy. Under some conditions, radar system can measure the direction, height, distance, course, and speed of these objects. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships, or other obstacles that are invisible to the naked eye because of distance, darkness, or weather. Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions. Basic design of radar system The following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver. Figure 2: Block diagram of a primary radar All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also-called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays. Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.

1. GROUP 2
Cdt. Carag
Cdt. Dizon
Cdt. Dumag
Cdt. Figuera

2. Basic RADAR – Operational
Principle

3. LO1.2 Explain the operational principle of
RADAR system

4. Operational Principle of RADAR
System
•Radar systems, like other complex
electronics systems, are composed of
several major subsystems and many
individual circuits. This section will introduce
you to the major subsystems common to
most radar sets. A brief functional
description of subsystem principles of
operation will be provided.

5. •A much more detailed explanation of radar
subsystems will be given in chapters 2 and 3.
Since most radar systems in use today are
some variation of the pulse radar system, the
units discussed in this section will be those used
in pulse radar. All other types of radar use some
variation of these units, and these variations will
be explained as necessary.

6. RADAR COMPONENTS
•Pulse radar systems
can be functionally
divided into the six
essential
components.

7. Synchronizer (Timer)
•The synchronizer ensures that all circuits
connected with the radar system operate in
a definite timed relationship. It also times the
interval between transmitted pulses to
ensure that the interval is of the proper
length. Timing pulses are used to ensure
synchronous circuit operation and are
related to the prf.

8. •The prf can be set by any stable oscillator,
such as a sine-wave oscillator, multivibrator,
or a blocking oscillator. That output is then
applied to pulse-shaping circuits to produce
timing pulses. Associated components can
be timed by the output of the synchronizer or
by a timing signal from the transmitter as it is
turned on.

9. Transmitter
•The transmitter generates powerful pulses of
electromagnetic energy at precise intervals.
The required power is obtained by using a
high-power microwave oscillator, such as a
magnetron, or a microwave amplifier, such
as a klystron, that is supplied by a low-power
rf source. The high-power generator,
whether an oscillator or amplifier, requires
operating power in the form of a properly-

10. •The high-power generator, whether an
oscillator or amplifier, requires operating
power in the form of a properly-timed, high-
amplitude, rectangular pulse. This pulse is
supplied by a transmitter unit called the
MODULATOR. When a high-power oscillator
is used, the modulator high-voltage pulse
switches the oscillator on and off to supply
high-power electromagnetic energy.

11. •When a microwave power amplifier is used,
the modulator pulse activates the amplifier
just before the arrival of an electromagnetic
pulse from a preceding stage or a
frequency-generation source. Normally,
because of the extremely high voltage
involved, the modulator pulse is supplied to
the cathode of the power tube and the plate
is at ground potential to shield personnel
from shock hazards.

12. •The modulator pulse may be more than
100,000 volts in high-power radar
transmitters. In any case, radar transmitters
produce voltages, currents, and radiation
hazards that are extremely dangerous to
personnel. Safety precautions must always
be strictly observed when working in or
around a radar transmitter.

13. Duplexer
•A duplexer is essentially an electronic switch
that permits a radar system to use a single
antenna to both transmit and receive. The
duplexer must connect the antenna to the
transmitter and disconnect the antenna from
the receiver for the duration of the
transmitted pulse.

14. •The receiver must be completely isolated
from the transmitted pulse to avoid damage
to the extremely sensitive receiver input
circuitry. After the transmitter pulse has
ended, the duplexer must rapidly disconnect
the transmitter and connect the receiver to
the antenna. As previously mentioned, the
switching time is called receiver recovery
time, and must be very fast if close-in targets
are to be detected.

15. •Additionally, the duplexer should absorb very
little power during either phase of operation.
Low-loss characteristics are particularly
important during the receive period of
duplexer operation. This is because the
received signals are of extremely low
amplitude.

16. Antenna System
•The antenna system routes the pulse from
the transmitter, radiates it in a directional
beam, picks up the returning echo, and
passes it to the receiver with a minimum of
loss. The antenna system includes the
antenna, transmission lines and waveguide
from the transmitter to the antenna, and the
transmission line and waveguide from the
antenna to the receiver.

17. Receiver
•The receiver accepts the weak echo signals
from the antenna system, amplifies them,
detects the pulse envelope, amplifies the
pulses, and then routes them to the
indicator. One of the primary functions of the
radar receiver is to convert the frequency of
the received echo signal to a lower
frequency that is easier to amplify.

18. •This is because radar frequencies are very
high and difficult to amplify. This lower
frequency is called the INTERMEDIATE
FREQUENCY (IF). The type of receiver that
uses this frequency conversion technique is
the SUPER HETERODYNE RECEIVER.
Superheterodyne receivers used in radar
systems must have good stability and
extreme sensitivity. Stability is ensured by
careful design and the overall sensitivity is
greatly increased by the use of many IF
stages.

19. Indicator
•The indicator uses the received signals
routed from the radar receiver to produce a
visual indication of target information. The
cathode-ray oscilloscope is an ideal
instrument for the presentation of radar data.
This is because it not only shows a variation
of a single quantity, such as voltage, but also
gives an indication of the relative values of
two or more quantities.

20. •The sweep frequency of the radar indicator
is determined by the pulse-repetition
frequency of the radar system. Sweep
duration is determined by the setting of the
range-selector switch. Since the indicator is
so similar to an oscilloscope, the term
RADAR SCOPE is commonly used when
referring to radar indicators.

21. Video

22. 10 Questions
Arial

23. Questions
1.What radar subsystem supplies timing signals to coordinate the operation of the complete system?
A.Synchronizer
B.Duplexer
C.Receiver
2.When a transmitter uses a high-power oscillator to produce the output pulse, what switches the oscillator on and off?
A.High-low voltage pulse from the modulator
B.Low-voltage pulse from the modulator
C.High-voltage pulse from the modulator
3.What radar component permits the use of a single antenna for both transmitting and receiving?
A.Synchronizer
B.Receiver
C.Duplexer
4.It receives faint echo signals from the antenna system, amplifies them, detects the pulse envelope, amplifies the pulses, and
sends them to the indicator.
A.Receiver
B.Synchronizer
C.Duplexer

24. 5.At exact intervals, the _______ generates intense pulses of electromagnetic radiation.
A.Transmitter
B.Duplexer
C.Receiver
6.It receives radar receiver signals and converts them into a visual indication of target
information.
A.Transmitter
B.Indicator
C.Receiver
7.What radar subsytem routes the electromagnetic energy from the transmitter, radiates it in
a highly directional beam, receives any returning echoes, and routes those echoes to the
receive?
A.Antenna System
B.Synchronizer
D.Transmiter

25. 8.This is an electronic system that uses reflected electromagnetic energy to detect the
presence and position of objects invisible to the eye.
A.Radar
B.ECDIS
C.Paper Chart
9.What is the use Synchronizer?
A.It generates electromagnetic energy in short, powerful pulses
B.It allows the same antenna to be used to both transmit and receive
C.It supplies the timing signals to coordinate the operation of the entire system.
10.The high-power generator, whether an oscillator or amplifier, requires operating power in
the form of a properly-timed, high-amplitude, rectangular pulse. This pulse is supplied by
a transmitter unit called?
A.Receiver
B.Modulator
C.Transmitter

26. Answers
1. A.Synchronizer
2. C.High-voltage pulse from the modulator
3. C.Duplexer
4. A.Receiver
5. A.Transmitter
6. B.Indicator
7. A.Antenna System
8. A.Radar
9. C.It supplies the timing signals to coordinate the operation of the entire
system.
10. B.Modulator